Appropriate solid state gain media for such a device must have absorption lines in the blue-violet wavelength region. Different crystalline host materials doped with rare earth ions have been already proposed as gain media for such solid state laser devices. The Pr3+-ion is of great interest in this context since it shows absorption at the typical emission wavelength of GaN-laser diodes and can convert this radiation into laser emission at blue, green, red and orange wavelengths.
U.S. Pat. No. 6,490,309 B1 discloses a solid state laser device in which a Pr3+ doped crystal is optically pumped by a GaN-based laser diode. The document proposes different Pr3+-doped crystals to obtain laser emission from Pr3+ at several visible wavelengths. The exemplary embodiments shown in this document are based on Pr3+ doped LiYF4 (YLF) crystals. Furthermore, laser emission of Pr3+ is reported to be obtained from the following hosts BaY2F8, Ba(Y,Yb)2F8, LaF3, Ca(NbO3)2, CaWO4, SrMoO4, YAlO3, Y3Al5O12, Y2SiO5, YP5O14, LaP5O14, LuAlO3, LaCl3, LaBr3, PrBr3, YVO4 and GdVO4. The solid state laser of this document is designed to work at only one of the several possible wavelengths emitted by the Pr-doped crystals.